The Approvals feature lets administrator define rules about which set of pages can accept edit submissions from read-only users.
Reviewers are then able to review the submissions and publish the changes.
An administrator must first create one or more approval rules in the Administration Area Approvals.
When a page matches an approval rule and a user is an allowed group, the Suggest Edits button appears in the top-right corner of the page:

Upon clicking it, the page switches to editor mode.
Assets Access / Upload
A user can only view and upload assets to folders allowed by the user group permissions. Guests cannot upload assets regardless of permissions.
When ready, click the Submit Edits button in the top-right corner to send the submission for review. If you're not logged in (and the Guests group is allowed to submit edits), you'll be prompted to provide a name and email address for attribution.
Users marked as reviewers for this page will be notified and will be able to review the submission.
As long as a submission is not approved or rejected, you can click the Suggest Edits button to keep editing your submission with further changes.
Reviewers can view active submissions in their Inbox page (click the button in the top-right corner), under the Pending Review tab.
Select a submission to view the proposed changes. You have the option to either Approve or Reject a submission. Upon approval, the page is updated with the proposed changes and they become part of the page history timeline.